Professor Mark Csele's Homebuilt Lasers Page

Other Lasers

Diode Lasers

This type of laser is easily built since all that is required is a suitable power supply. A simple current-regulator is required to energize the diode. These are fairly robust devices but are easily damaged by overcurrent ... even for a short time ... so a proper regulator is really needed. Inexpensive laser pointers do not even use an active regulator - the 'dollar store' variety I've seen simply use a series resistor!

Both red and infrared diode lasers can be scavenged from old handheld barcode scanners, CD players, laser printers, laser pointers, etc. Once removed, hopefully they have numbers which can be cross-referenced the part number on the manufacturer's site to determine it's characteristics - most importantly maximum current!

Diode Laser from a Scanner One such laser scavenged from a handheld bar-code scanner was a Sharp laser diode emitting at 780 nm and having a rated output of 5mW. The maximum current was specified (on the data sheet) at 60mA so a simple current regulator, set for 55mA using an LM317T voltage regulator with a series resistor between the output and adjust terminals, was constructed. This simple regulator has only a few parts and does not use the internal photodiode. The photodiode, incidentally, exists on virtually all laser diodes and is the third terminal on the laser diode package. It is designed for feedback to maintain constant light output as the device heats during operation. For simple non-stabilized applications it is not required although intensity of the laser beam will tend to wander as the laser heats during use. Note that the diodes in many cheap red laser pointers (i.e. the under $10 variety) also lack photodiodes. One inexpensive unit, which ran from three small watch batteries, employed nothing more than a surface-mounted resistor for current limiting - no active drive circuitry whatsoever.

Laser Diode Power Supply
The simple drive circuit here uses a fixed-voltage regulator wired as a current regulator. The regulator attempts to maintain a fixed voltage between the ground and Vout terminals - in this case 5 volts. Using ohms law the current is determined to be 5 V / 100 Ohms = 50 mA. By selecting the appropriate resistance the diode current can be set to any desired value.

Without an active drive circuit, laser diodes may be used in a variety of experiments for determining lasing threshold. Experiments on a diode to determine threshold current may be perfromed by connecting it to a lab type current-regulated power supply. If an IR diode is used, an IR detector card must be used to observe the output. As current is slowly increased from 0 to 60mA the optical output will be seen to begin as an unfocussed 'blob' of light appears. This is spontaneous, not laser, emission and is similar to the light that a regular LED emits. As current is increased a tight beam begins to appear. This is the laser output and should appear by 30 or 40mA. Usually the maximum current for an IR diode is between 50 and 60 mA so be careful not to blow the diode when experimenting.

Laser Diode Threshold, Diagram Copyright John Wiley & Sons, 2004
Figure 1: Laser Diode Threshold (Diagram Copyright John Wiley & Sons, 2004, used with permission)

Cheap Laser Pointer Cheap Laser Pointer Laser pointers are a cheap source of visible diodes. This particular unit, purchased for $5.50 CDN, runs from three button cells. Once the battery cover was unscrewed a small screwdriver was used to push the entire laser assembly forward breaking a (weak) epoxy dot holding it in the tube. The laser itself is a 'bare' diode with no feedback. The 'driver' is nothing more than a surface-mounted resistor to limit current to about 55mA (with 4.5V at the battery terminals).

Red Diode Laser This rear view of the scavenged laser diode shows the spring which makes contact with the batteries (negative terminal), pushbutton switch, and the laser itself. The laser is seen here glowing red (most emission is forward towards the collimating lens). It is about the size of a grain of salt. Be sure NOT to solder the positive terminal onto the circuit board directly beneath the diode or you will surely overheat it ... attach the wire mechanically via a round crimp-on terminal.


Mercury-Vapour Ion:

What makes this laser, which emits two lines in the green and red-orange, unique is that it is an ion laser with a large gain. Laser tubes tend to be long: on the order of 1 metre in length. Most references mention the use of (expensive) dielectric mirrors however there are a few which do mention that the gain of the green line is so high that (cheap) aluminum mirrors may be used (i.e. One mentions that 70% reflection seems to be enough)! An interesting approach might be the conversion of a HeNe laser tube - one with external optics would certainly be viable but even internal optics might work (although the lifetime of the tube would likely be short cue to ion bombardment of the delicate mirror coatings). A rather exotic vacuum system is likely required since pressures are low. Looks to be somewhat 'fussy' to build but probably still within the grasp on a dedicated amateur.

A few key references:

A homemade mercury-vapor ion laser that emits both green and red-orange
Scientific American, Amateur Scientist Column, Oct. 1980
A good starting point.

Visible Laser Transitions in Hg+ W. E. Bell
Applied Physics Letters, Vol. 4, No. 2, 15 Jan. 1964
A description of the laser, mechanism of excitation, and gain.


Copper Chloride:

A metal-vapour laser producing simultaneous green and yellow output. High temperatures are required to keep the metal-vapour pressure high enough to lase (about 400C) and a simple vacuum system capable of maintaining a 2 torr vacuum. Otherwise, looks reasonable for the amateur to construct since it is a high-gain laser (so optics aren't critical nor expensive) and lacks any very critical components.

A few key references:

A homemade copper chloride laser emits powerful bursts of green and yellow light
Scientific American, Amateur Scientist Column, April 1990
An excellent article describing one amateur's design

Double-discharge copper vapor laser with copper chloride as a lasant C.J. Chen, et al.
Applied Physics Letters, Vol. 23, No. 9, 1 November 1973, pp. 514
One of the first reports of a laser of this type.

A parametric study of the copper chloride laser Noble M. Nerheim
Journal of Applied Physics, Vol. 48, No. 3, 1977, pp. 1186
A good study outlining the parameters affecting this laser. Required reading for anyone attempting to build one of these beasts.


Carbon-Dioxide (CO2):

MPB Carbon-Dioxide Laser, Photo Copyright M.Csele, 2003

Considering this is a high-power CW laser it looks quite simple to construct. While I have never built one from scratch but there are numerous pages on the web describing various lasers built by others. As well as the 150 Watt laser above, I maintain a 50 Watt CO2 laser we use at the college for thick-film resistor trimming. A Coherent model 42 built in the 1970's, it is still a good laser but occasionally requires TLC such as cleaning and aligning optics as well as work on the power supply (which uses two large type 250TH vacuum tubes as current switches).

The CO2 laser The cooling jacket and tank of pre-mixed gas is seen here.
The business-end of the CO2 laser The output coupler is in the white ring to the left.

A few key references:

A Carbon Dioxide Laser Is Constructed By a High School Student In California
Scientific American, Amateur Scientist Column, Spetember 1971
An excellent article describing a simple design which I've seen duplicated many times